DESCRIPTION ( Adapted from applicant's abstract): The neural basis for the generation and control of vertical vestibular-induced eye movements, including the adaptive plasticity of the vestibulo-ocular reflex will be studied utilizing physiological, neurochemical and morphological techniques in squirrel monkeys. The vertical vestibulo-ocular reflex will be visually adapted by employing visual-vestibular mismatch stimuli and/or miniaturizing or magnifying lenses placed in a spectacle mount in front of the animals' eyes. Both the normal and adapted vestibulo-ocular reflex will be utilized as behavioral probes to elucidate the properties of discharge modulation of cerebellar floccular Purkinje cells and brainstem neurons. Previous work suggested that there are multiple brain sites for vestibulo-ocular reflex learning and memory, namely in the cerebellum and brainstem. We will adapt the vertical vestibulo-ocular reflex gain with paradigms designed to elucidate which of these sites encode signals that might be causal to the observed behaviors. We will also analyze the firing patterns of Purkinje cells by chemically inactivating sites known to carry components of the input signals to these cells., We will test our hypothesis that a major function of the cerebellum is to stabilize the vestibulo-ocular reflex during parametric gain changes. Our experiments should provide definitive data to discriminate between extant models of cerebellar function.